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Radar System

Bistatic Speed Sensor

BISTATIC SPEED SENSOR — CW DOPPLER RADAR SEPARATE TX AND RX ANTENNAS TX ANT RX ANT CW SOURCEOscillator TX LNALow Noise MIXER LPFDoppler AMPIF Gain DSPFreq Counter LO TAP TX/RX ISOLATION: ANTENNA SEPARATION + FREE SPACE PATH LOSS (TYPICALLY 40-60 dB)
Component Descriptions

Signal Chain Walkthrough

The bistatic configuration uses physically separate antennas for transmit and receive, eliminating the circulator entirely. TX/RX isolation is achieved through antenna separation and spatial filtering rather than a ferrite device.

Separate Antennas

The TX and RX antennas are physically separated, providing 40-60 dB of isolation depending on spacing, antenna directivity, and cross-polarization. This dramatically reduces TX leakage into the receiver compared to monostatic designs.

CW Source with LO Tap

The oscillator output drives the TX antenna through a PA (if needed). A coupled or split portion of the source signal serves as the LO for the receive mixer, maintaining coherent detection capability.

Receive Chain

RX antenna feeds the LNA, which amplifies the weak echo. The mixer produces the Doppler beat frequency. LPF, amplifier, and DSP extract the target velocity from the Doppler spectrum.

Typical Specifications

Component Specifications

ComponentParameterTypical Value
CW SourceFrequency10 - 77 GHz
CW SourceOutput Power+5 to +20 dBm
TX/RX IsolationAntenna Separation40 - 60 dB
LNANoise Figure1.0 - 3.0 dB
LNAGain15 - 25 dB
MixerConversion Loss6 - 10 dB
Design Note: Bistatic isolation is proportional to antenna spacing and their mutual coupling. For closely-spaced antennas (same housing), use orthogonal polarization or absorber baffles between antennas to increase isolation. The bistatic angle between TX and RX antennas introduces a cosine factor in the Doppler equation that must be accounted for in velocity calculations.
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